In vitro activity of sitafloxacin against atypical bacteria (2009-2014) and comparison between susceptibility of clinical isolates in 2009 and 2012.

: In vitro activities of sitafloxacin (STFX) along with fluoroquinolones (levofloxacin (LVFX), moxifloxacin (MFLX), garenoxacin (GRNX)) and macrolides (azithromycin, clarithromycin) against atypical bacteria (Mycoplasma pneumoniae, Legionella pneumophila, Chlamydia trachomatis, Chlamydophila pneumoniae) recovered from clinical specimens from 2009 to 2014 at different healthcare facilities in Japan were investigated. The minimum inhibitory concentration of STFX at which 90% of isolates (MIC₉₀) against M pneumoniae (n= 14) was 0.03μg/mL which was comparable to GRNX, 4- and 16-fold more active than MFLX and LVFX, respectively. Reduced susceptibilities of M pneumoniae (9/14 isolates) to macrolides were observed. MIC₉₀ of STFX against L. pneumophila (n =15) was 0.004μg/mL which was 2- and 4-fold more active than GRNX/LVFX and MFLX, respectively. The minimum inhibitory concentration range of STFX against C. trachomatis (n=5) and C. pneumoniae (n=5) were from 0.015 to 0.03 and from 0.03 to 0.06μg/mL, respectively. Furthermore, differences between the activities of STFX against various clinical isolates in 2009 and those in 2012, which were already published in two articles (Jpn. J. Antibiotics 63:411- 430, 2010, 66:311-330, 2013), were also evaluated. The MIC90s of STFX against methicillin- susceptible Staphylococcus aureus (MSSA), Streptococcus spp. and Enterococcus faecalis isolated in 2012 were 4 or 8 times higher than those in 2009, however there was no difference between STFX activities against other species in 2009 and those in 2012. In conclusion, STFX showed potent activity against atypical bacteria (M pneumoniae, L. pneumophila, C. trachomatis, C. pneumoniae) and no tendency for emergence resistance to Gram- positive cocci, Gram-negative bacteria and anaerobes except MSSA, Streptococcus spp. andt. faecalis.